**Solution:**

To find the freezing point of the solution, we need to calculate the change in freezing point caused by the presence of the solute.

**1. Calculate the change in freezing point (∆Tf) using the formula:**

∆Tf = Kf * molality * i

where Kf is the freezing point depression constant for water, molality is the molal concentration of the solution, and i is the van't Hoff factor.

**2. Calculate the molality (m) of the solution:**

Molality (m) is defined as the number of moles of solute per kilogram of solvent. In this case, the solute is the weak acid and the solvent is water.

Molality (m) = moles of solute / mass of water solvent in kg

Since we are given that the solution is 0.1 molal, we can assume that the moles of solute is equal to 0.1 moles.

**3. Calculate the van't Hoff factor (i):**

The van't Hoff factor (i) accounts for the number of particles formed when the solute dissolves in the solvent. For a weak acid, such as the one in this solution, the van't Hoff factor can be assumed to be 1, as the acid does not dissociate completely.

**4. Substitute the values into the formula for ∆Tf:**

∆Tf = Kf * molality * i

Substituting the given values:
Kf = 1.86°C/m
molality (m) = 0.1 molal
i = 1

∆Tf = (1.86°C/m) * (0.1 molal) * (1) = 0.186°C

**5. Calculate the freezing point of the solution:**

The freezing point of the solution can be calculated by subtracting the ∆Tf from the freezing point of pure water.

Freezing point of solution = Freezing point of pure water - ∆Tf

Since the freezing point of pure water is 0°C, the freezing point of the solution will be:

Freezing point of solution = 0°C - 0.186°C = -0.186°C

Therefore, the freezing point of the 0.1 molal aqueous solution of the weak acid is -0.186°C.